The present invention concerns a process for forming tunnels, splitting stones and especially cap or shell-splitting rocks or splitting of rocks preferably to pre-worked, square blocks, or blocks with at least one straight or plane surface. The invention also concerns a tool for performing the process.
When splitting stone blocks it is common to drill a row of parallel holes with a regular distance from each other where the splitting/parting is to take place. Explosives, expanding chemical substances or compositions and/or different types of splitting tools have conventionally been used to split rocks.
When rocks are split with explosives the explosive is filled into the previously bored holes in the rock and are detonated to loosen/split the block. Such explosive charges will also preferably be detonated simultaneously to loosen the block, and the determination of the quantity of explosives or explosive charges must be done with utmost care and precision to avoid blowing the block to pieces. Additionally, when working with natural rock or decorative stones or slabs, the stone may be damaged by the explosion, and when working with explosives there is also a risk of personnel injuries. The drawbacks with explosives are obvious since this creates a large amount of cracks. Invisible flaws may not appear until after the stone is split with explosives. Furthermore, this creates smaller or larger cracks in the stone masses left after the explosion. This is dangerous work wherein the quality of the result is at best uncertain.
When splitting rocks with expanding chemical substances or compositions, such substances will initially be filled into the bore holes and subsequently exert their expanding effect on the rock. This method is much more controllable than and less stringent than splitting the rock with explosives, but also here it is necessary to carefully measure and add the correct amount of expanding material to overcome the tensile strength of the rock, and additionally some post-handling of the split stone material will be necessary. Additionally, the splitting of rock with an expanding chemical material will be time-consuming, and this is poorly suited for use in an effective stone quarry.
When using wedges for splitting rocks according to the prior art, wedges are gradually driven into the bore holes. The driving of wedges will frequently be done with the use of a sledgehammer/pneumatic piledriver and eventually the wedges will overcome the tensile strength of the rock, resulting in the rock splitting.
The most common way to drive the wedges manually into the rock is by predrilling the splitting holes as indicated supra. A number of wedges are then placed inside the predrilled holes, and they are then driven sequentially and manually into the holes by starting the splitting at one edge of the rock, driving the wedge nearest to the edge into its hole, then driving the next wedge in the hole adjacent to the first one downwards into its hole, etc; and when reaching the farthest edge of the rock repeating the driving sequence until a slab is split from the rock. This manual splitting is obviously very time-consuming and cumbersome, and it is difficult to split rock slabs off from the mother rock beyond the reach of the wedge or splitting tool.
Work with different types of splitting tools are also associated with danger, albeit less than when using explosives, and such splitting of rock may also be used under conditions where blowing-up the rock with explosives is neither possible or nor suitable. However, the splitting of the rock puts certain demands on the splitting tool, and the splitting of slabs or blocks of rock has until today been difficult because it has not been possible to guide the splitting of the rock sufficiently by using conventional splitting tools.
In Norwegian patent 13.161 there is shown a splitting tool wherein a gliding wedge is compounded with a piston rod in the centre axis of a hydraulic cylinder, and wherein two or more insert pieces with a circular cross section are connected with the cylinder housing. The insert pieces have angular surfaces which downwards forms a narrowing wedge space. There arise tensile forces in the stone block from the bore hole when the sliding wedge gradually is pressed into the wedge space by using hydraulic pressure. The drawback with this tool lies inter alia in the location of the sliding wedge in the centre of the tool, since this makes it impossible to split thin slabs off stone blocks and it is furthermore impossible to split off slabs farther down the slab than the length of the wedge tool. Each wedge is additionally a very heavy unit and is poorly suited for any practical production of natural stone slabs or working in tunnels. In addition the wedges must have a suitable hydraulic aggregate on account of the high pressure which is necessary to build up in the tool, a pressure which depends on the rock type which is to be split, and which with rock types with a large tensile strength may be relatively significant.
Another drawback with a splitting tool which formerly is known from Norwegian patent 113.161 is that such a tool comprises a central piston rod in the wedge and which passes the insert pieces placed in the drilled hole in the rock to be split. Since the central piston rod in the wedge passes the insert pieces, which consequently are pushed aside and pressed against the sides of the drilled hole, the piston rod may easily become stuck in the bottom of the drilled hole or it may break, something which in turn leads to a reduced efficiency because inordinately long drilling holes must be drilled when using this type of tool. Additionally the wedge disclosed in this prior art patent, is not able to split the rock in close proximity to a surface on account of the total circumference of the cylinder being significantly larger than the wedge itself. Furthermore it is a drawback that all of the force from the wedge is distributed over a very small surface so that the rock consequently may be damaged in the breaking zone and lead to a poor product.
It is known from Norwegian patent 172.260 a tool for splitting rocks wherein the tool comprises a securing bolt to be introduced into a predrilled hole in the stone block. The splitting tool comprises additionally an arm mechanism being guided by a hydraulic cylinder with an impingement point against the stone block at a given distance from the drilled hole, and which also works as an anchorage point for the securing bolt of the tool. When supplying hydraulic oil to the hydraulic cylinder, the tool is given a pushing force from the impingement point on the stone block so that a tilting movement arises in the tool. This has as a consequence that the securing bolt is tilted against the adjacent sides of the drilled hole so that tensile scissoring forces arise in the rock. The drawback of such a splitting method is that the wedge will have a point-formed breaking force so that there arises a large degree of deformations around the breaking point, and when splitting thin slabs there will be created a very irregular block form in the product since the wedges exert force against the surface instead of creating initial cracks against the drilled hole at its side. Blocks with such an uneven form are not desirable for potential receivers of the raw blocks.
U.S. Pat. No. 5,020,859 discloses a splitting tool designed so that the wedges are not produced with so small a diameter so that they may be used for producing natural rocks or in the entrepreneur trade. An example given in this patent is based on drilling holes with a diameter over 105 mm, something which is unsuitable for slab-splitting thin stone slabs. In addition this tool is meant to split[ting of] materials with a very high cohesive strength, e.g. for destroying armed concrete.
For splitting stone having been equipped with a number of drilling holes being located along a substantially straight line and being substantially straight along the axis of the drilling holes, a tool is thus required giving impingement points which mainly lie diametrally across from each other inside the drilling hole. It is also an advantage that the splitting force is located far inside the drilling hole.
Such splitting of rocks as disclosed supra is called shell or slab-splitting. The slab-splitting of today is otherwise done mainly manually and with a sledgehammer, wedge and wedge holders, and this is often a dangerous and cumbersome work. There has also been developed a hydraulic/pneumatic tool for such slab-splitting wherein a hydraulic/pneumatic power hammer, however, working within the same principles as manual splitting, this method has not had any development or been refined within the last 30 years. Consequently there is a need for an improved, safer and less cumbersome method for splitting rocks wherein the safety is better and wherein the waste percentage may be reduced.
In the Norwegian and foreign block stone industry of today there is a need for a tool which covers all the needs for working rocks in such a way that it is to a large extent possible to avoid explosives completely. There exists a particular need for a tool which may be used for slab-splitting, a process which is most work-consuming within the stone block industry and which also is the working form which causes most injuries to the working personnel.
With the present invention there has been produced a process for splitting rocks wherein there has been pre-drilled a number of holes in the rock, and wherein the holes preferably mainly lie along an imaginary line in the rock. The splitting tool being used in the process comprises wedge holders which are placed inside one or more of the drilling holes in the rock, wherein the points of attack for the wedge holders for splitting the rock lie mainly adjacent each other in the drilled hole and where the wedge holders are oriented parallel with the imaginary line between the drilled holes, the splitting tool with the wedge holders expand more than the diameter of the drilled holes when the expanding force being supplied to between the wedge holders surpasses the tensile strength of the rock so that there is created initial cracks between the drilling holes, where these cracks are expanded downwards along the axis of the drilled holes in the rock by the further expansion of the wedge. As disclosed supra this is achieved when the rock which is to be split is supplied with at least one hole wherein there may be introduced a number of wedges. By placing one or more wedges inside the hole the wedging force will work radially outwards in the hole with points of attack mainly across from each other inside the hole, and the rock will be forced apart by the creation of cracks in the rock where the cracks run mainly along the axis of the drilled holes, by the wedge pressing the wedge holders apart to a diameter surpassing the diameter of the respective predrilled hole and which surpasses the tensile strength of the rock. In this way blocks may be split from the rock wherein the holes have been drilled. In the process according to the invention the wedge holders 11,12 are pressed towards the periphery of the drilled hole with the back zz of the wedge against the inner wedging surface xx. When the hydraulic/pneumatic pressure becomes greater than the tensile strength of the stone, an initial crack will be created between the two adjacent holes, which will extend and at last create an open crack along the imaginary line between the holes, where the rock wall left in the stone block is called the inner surface xx, and the other rock wall which becomes removed, is called the outer surface yy. The process according to the invention is further distinguished by being performed with a tool as disclosed infra, where the wedge holders press against the periphery of their relevant hole so that the outer surface yy is broken away and the inner surface xx is left, where the spine of the wedge will follow the inner surface xx and remove the rest of the rock material in a successive sequence of the one disclosed supra.
By placing a number of wedges successively in rows and successively pressing the wedge holders radially apart it is in principle possible to split as large stone blocks as wanted by this method. In practice, however, there will be limitations on the method in that it will not be possible to split blocks of an unlimited size, but these limitations will be obvious to the person skilled in the art based on the knowledge of the nature of the relevant rock, or they may be determined by conventional and simple tests. By staying within the practical upper limits for such splitting of rocks the above indicated problems may, however, easily be avoided.
When splitting rocks the natural rocks, fall into three main groups: Block stone (types of gneiss and granite), slate and marble.
Block stone is produced from rock types which may be broken in large blocks and are formed in rectangular and quadratical shapes for further work-up such as for building purposes and monuments. In Norway this is not used to any large extent domestically, so most of the material is exported with a price established per cubic meter. E.g. when working with larvikitt which has a waste percentage of about 95%, 1% less waste will mean about 20% more material to be sold. Normally the waste percentage in workable quarries will be up to 98%. The reduction of this waste percentage is one of the advantages with the present splitting method and tool.
Concerning slate, the process and device according to the present invention gives a new and better opportunity to use less explosives and thus reduces the waste percentage. Slate deposits are worked by there first being split off a large stone block from the mountain. When the block has been loosened, the final slate slabs are produced by drilling and splitting. By using the process and tool according to the invention the person working the quarry will get a better total economy on account of a lower waste percentage and a better efficiency.
In addition to the production of block stone the process and tool according to the invention may also be used for e.g. expanding tunnels, be it train tunnels, water tunnels or other kinds of tunnels where explosives may not be used, and the method and tool may also be used if there exist a need for splitting rocks at other places where explosives may not be used, such as in highly populated areas.
The same method being disclosed supra for block stones and slate may also be used xe2x80x9cfor splittingxe2x80x9d marble.
The present invention also concerns a tool which may be used in the process according to the invention for splitting rocks, e.g. in controlled splitting of loose blocks of rock. Loose blocks of rock are often found on agricultural properties and on industrial and domestic house sites.
Both the process and the tool according to the invention may be used where a controlled splitting of rocks is wanted independent from what kind of rocks are split or what kind of splitting is wanted, be it splitting of block rocks, slate, marble, or when expanding tunnels etc..
An embodiment of a tool according to the invention will be disclosed infra with reference to the enclosed FIGS. 1-3a-d.